我国研制出世界目前最薄钙钛矿二维材料。钙钛矿的主要化学组成为钛酸钙。如图是钙、钛、氧元素在元素周期表中的相关信息。下列说法正确的是() A . 钙原子的核外电子数为20 B . 钛元素的相对原子质量为47.87g C . 钙、钛、氧的质子数依次减小 D . 三种元素都是金属元素 答案:A After the new technique was
introduced, the farmers produced ________ grain in 2006 as five years before.
A. as twice much B. as
much twice C. twice much as D. twice as much